1. Field of the Invention
The present invention refers to a cloverleaf microgyroscope and a method of manufacturing a cloverleaf microgyroscope that contains a single crystal silicon cloverleaf-shaped resonator and integrated post attached to the leaves with through-wafer interconnects.
2. Description of Related Art
U.S. Pat. No. 5,894,090 to Tang et al., which is incorporated herein by reference, discloses a micromachined symmetrical leaf structure having a plurality of symmetrically disposed leaves about a defined center. At least one micromachined spring is disposed symmetrically with respect to the symmetrical leaf structure and supporting the symmetrical leaf structure, a rim/base structure to which the spring is coupled. The rim/base structure includes a plurality of sensing and drive electrodes and a circuit electrically coupled to the electrodes included within the rim/base structure. The circuit provides drive signals to the drive electrodes to oscillate the symmetrical leaf structure and to receive a sensing signal from the sensing electrodes to detect response of the oscillating symmetrical leaf structure to physical phenomena exterior to the micromachined resonator. The micromachined resonator has a manually inserted post. It shows a lack of a silicon based vacuum encapsulation. A low yield is obtained during the separation. The manufacturing of the resonator involves high fabrication costs. It shows large vibration sensitivity and no clear path to electronic integration.
The known manufacturing processes make it very difficult to manufacture a microgyroscope. The central post is inserted by hand, the device has to be vacuum packaged in a custom package and there is no ability to integrate control electronics with the silicon structure.
Although electrical through-wafer vias have been used for many years for standard ICs, the use of deep (>500 microns) vias with MEMS within a wafer-level vacuum package has not been attempted to our knowledge. In addition, standard pn junction techniques for electrical isolation are not satisfactory for the extremely high levels of isolation that must be achieved for MEMS devices. Also, standard poly fills of etched vias are not useful since the front side contacts (control electrodes for the MEMS device) must be perfectly smooth for the microgyro. This is needed to produce a high degree of reproducibility of the measured capacitance between the plates. The use of spray resist techniques allows us to perform lithography in high-aspect ratio holes, and thus create the desired structure.
What are needed are a cloverleaf microgyroscope and a process for manufacturing a cloverleaf microgyroscope with an integrated central post and electronics with the resonator and vacuum package at wafer-level with a single crystal silicon construction.